1. Field of the Invention
The present invention relates to random copolymers comprising a C.sub.4 to C.sub.7 isomonoolefin and an alkenylstyrene comonomer, and functionalized derivatives thereof.
2. Description of the Related Art
Halogenated copolymers of isobutylene and up to about 4 mole % of isoprene (butyl rubber) are well known polymer materials whose vulcanizates offer some outstanding properties not possessed by many other diolefin based elastomers. Articles prepared from many cured halogenated elastomers offer improved resistance to oils and greases as well as resistance to oxygen and ozone degradation. Butyl rubber vulcanizates exhibit excellent impermeability to air, water vapor and many organic solvents, as well as resistance to aging and sunlight. These properties render these materials ideal candidates for one or more applications such as tubeless tire innerliners, water hoses, organic fluid hoses, components in tire construction, gaskets, adhesive compositions and various molded articles.
More recently, a new class of halogenated elastomeric interpolymers have been discovered as disclosed in U.S. Pat. No. 5,162,445, which offer many of the same properties as halogenated butyl rubber, but are even more ozone and solvent resistant. These materials are the halogenation product of random copolymers of a C.sub.4 to C.sub.7 isoolefin, such as isobutylene (IB) and a para-alkystyrene comonomer, such as para-methyl styrene (PMS), wherein at least some of the alkyl substituent groups present in the styrene monomer units contain a functional group such as halogen. The prepared copolymers exhibit homogeneous incorporation of the comonomer over the entire molecular weight range making functionalization equally homogeneous. The benzylic position on the PMS fragment may be selectively functionalized to a variety of groups such as esters, bromides, ethers, thioethers, etc. Additionally, graft copolymers may be prepared. Functional modification of the parent copolymers leads to elastomers with interesting and useful properties. Many of these are disclosed in the '445 patent, in U.S. Pat. No. 5,430,118 and in U.S. Pat. No. 5,426,167. The most important utility of the halogenated copolymers is that the benzylic halide presents new opportunities in crosslinking chemistry while improving oxidative stability of the resulting rubber. The oxidative stability results from the absence of backbone double bonds found in the copolymerized products of conjugated dienes, as in the case of butyl rubber.
Low molecular weight IB/PMS copolymers are attractive copolymers for sealant and coating applications. They offer the inherent attributes of polyisobutylene as well as good weatherability because of the absence of in-chain unsaturation. In addition, versatile functionalization chemistry permits the introduction of a wide variety of functional groups. For example, vinyl groups can be introduced two ways. Metallation of the p-methyl group provides for reaction with electophiles like vinyl chlorosilanes or allyl chloride to yield pendant vinyl groups. Alternatively, IBIPMS copolymers can be halogenated to the benzylic halide and then reacted with the sodium salt of allyl alcohol to yield an allyl ether. Regardless of the process, the introduction of pendant vinyl groups requires at least two post-polymerization steps. It would be advantageous to prepare alkenyl containing IB copolymers by direct copolymerization of the appropriate comonomers.
Vinylbenzyl chlorides have been used as comonomers for IB copolymerization.
U.S. Pat. No. 3,067,182 discloses the copolymerization of 70 to 99 mol% of IB with 30 to 1 mol% of, preferably, para isopropenylbenzyl chloride (IPBC) in an inert 30 solvent using a Friedel-Crafts catalyst, and at a temperature below -50.degree. C. A continuous polymerization method for copolymerizing vinylbenzyl chloride (VBC) (a mixture of meta- and pra-substitution) and isobutylene is disclosed in U.S. Pat. No. 4,074,035. This process necessarily restricts the incorporation of VBC to less than 5 mol% and requires a well-controlled continuous addition of comonomer within a precise range of comonomer ratios in order to prepare gel-free polymers. A similar system is discussed for ortho- and para- mixtures of IPBC in Jones, et al., J Appl. Polym. Sci. 5, 452 (1969).
Allyl halides have also been used as functional monomers in IB copolymerization. Methallyl chloride is used in U.S. Pat. No. 3,299,020 as a comonomer, but the copolymer is said not to contain allylic halides and therefore does not exhibit enhanced cure characteristics. In essence the functional group is lost. Chlorobutyl rubber preparation from methylallyl chloride or 2-chloromethyl-1,3-butadiene is disclosed in Sadykh-Zade et al. in Dokl. Akad Nauk, Azerb. SSR 24, 20 (1968) under conventional cationic polymerization conditions. Up to 2 mol% of the allyl chloride is incorporated into the copolymer. Homologous comonomers are used for halobutyl rubber preparation in U.S. Pat. No. 5,342,908.
Pendant groups, like vinyl alkenyl and allylic, present another class of reactive "functional" groups which are of utility in modifying polymer. These groups are more nucleophilic than backbone vinylene and vinylidenes (March, Advanced Organic Chemistry, 4.sup.th Ed., John Wiley & Sons, New York, 1992, page 748) formed by copolymerization of conjugated dienes. Pendant alkenyl groups permit reactive crosslinking, and grafting and chemical modification. Many of these reactions occur by simply heating the reagent with the virgin polymer. This process does not create unwanted side products (like halogens) that must be removed from the polymer before use. Preparation of pendant alkenyl groups from the methodologies described above would require post-polymerization functionalization.
Direct copolymerization of alkenyl styrenes would present a novel method of incorporating such pendant alkenyl groups into polyisobutylene. From this class of comonomers, two have been previously prepared and used in anionic polymerizations; p-allylstyrene (K.C. Frisch, J Polym. Sci. 41, 359 (1959); G.F. D'Alelio, T.R. Hoffend, J Polym. Sci., Part A-15, 1245 (1967); and von G. Greber, G. Egle, Makromol. Chem. 54, 119 (1962)) and p-3-butenylstyrene (von Greber, ibid.). The G.F. D'Alelio reference notes in the Synopsis that "crosslinked polymers were obtained when radical and cationic initiators were used". This point is further illustrated with conmnents on page 1253 and data in Table 3 on page 1254. These references teach that cationic polymerization of said monomers to non-crosslinked polymers is not possible. No teaching of the utility of these types of comonomers with isobutylene is disclosed.